For analysis of samples, for example of body fluids such as blood or urine, test element analysis systems are often used in which the samples to be analyzed are located on a test element and, if appropriate, react with one or more reagents on the test element before they are analyzed. Optical evaluation, in particular photometric evaluation, of test elements is one of the most common methods for rapid determination of the concentration of analytes in samples. Photometric evaluations are generally used in the field of analysis, environmental analysis and, above all, in the area of medical diagnostics. Test elements which are evaluated by photometry have great importance in particular in the area of blood glucose diagnosis from capillary blood.
There are various forms of test elements. The main examples are square panels, also referred to as slides, at whose centre a multi-layer test field is situated. Diagnostic test elements of strip-shaped configuration are referred to as test strips. Test elements are described widely in the prior art, for example in documents DE-A 197 53 847, EP-A 0 821 233, EP-A 0 821 234 or WO 97/02487. The present invention concerns test elements of any form.
The positioning of the test elements in the test element analysis system is of great importance both for the accuracy of the analysis and for the ease of handling. One objective in carrying out analytical tests is to reduce the amounts of sample used, and to permit reliable analysis even when only small amounts of sample are present. In the area of blood glucose analysis, a drop of blood has to be taken from part of a person's body, and it is more convenient if the amount of blood needed for the test is as small as possible. A reduction in the amounts of samples is associated with decrease in the size of the test elements and in particular of the detection zones present on the test elements. To ensure an exact analysis of the sample, precise positioning of the detection zone in the test element analysis apparatus is necessary. Inaccurate spatial orientation of the test element leads directly to a decrease in the effective measurement surface and can therefore lead to a measurement error.
A large number of positioning devices for test elements are known in the prior art. EP-B 0 618 443 discloses a test strip analysis system in which a positioning of the detection zones of the test element takes place both laterally and also vertically with respect to the measurement optics, by using a bending axis transverse to its longitudinal axis and parallel to its surface. Further positioning devices for test elements can be taken for example from documents DE-A 38 44 103 or from EP-A 0 319 922.
These positioning devices cited as examples from the prior art are suitable for positioning and subsequent reliable analysis of test elements with detection zones whose size exceeds 5 mm×5 mm. If the detection zone is smaller, however, in its lateral extent, the positioning of the test elements with the aid of these positioning devices from the prior art is not sufficiently precise.
A positioning device for test elements from the prior art which permits reliable evaluation of test elements with smaller detection zones is known from document WO 00/19185. In order to hold the test element in the evaluation position, this positioning device comprises a displaceably mounted journal with a downward conically tapering end. Upon suitable positioning, the tip of the journal is situated in a recess in the test element, so that the test element is fixed in the direction of its longitudinal axis and positioned. The journal can also serve to electrically signal the presence of a test element and its positioning. For this purpose, the journal is made electrically conductive, and a contact is provided on the side of the device lying opposite it. Without a test element, the journal is pressed towards the contact by means of a spring, and an electrical contact is established between these two elements. If a test element is now inserted, it is first pushed in between journal and contact, so that the electrical contact is cancelled. When it is pushed in farther, however, the journal engages through the groove of the test element and the electrical contact closes again. A disadvantage of this positioning device is that it is costly to produce, because many electrical contact points are needed, these being produced by complex surface coating. Moreover, several component parts of the positioning device (for example the journal) assume both electrical and also mechanical functions, so that different demands are placed on the material from which they are made. For example, parts made of a combination of metal and plastic have to be used. Another considerable disadvantage of this positioning device known from WO 00/19185 is that the contact towards which the journal is pressed can be rapidly soiled by the sample. The sample located on the test element may, for example, pass through the recess in the test element and get to the contact.
Therefore, the object of the present invention is to avoid said disadvantages of the prior art and to make available a positioning device for test elements, a test element analysis system, and a method for positioning test elements, all of these permitting reliable evaluation of test elements with small detection zones. A functional separation between mechanical aspects and electrical aspects should also be permitted in the positioning device. The positioning of the test element is to be electrically signalled by low-tolerance transmission of the switching function to a remote printed circuit board.